Pulp screening machine



July 5, 1938.

Filed Jan. 3, 1956 4 Sheets-Sheet 1 as 93 ,2s 27 lnvenTov Neson MKnghT www 2.7M

July 5, 1938. N. M. KNIGHT 2,122,475

PULP SCREENING IACHINE 'Filed Jan. s. 1936 4 sheets-sheet 2 Invnor. Nelson M Knigh bya/JMM July s, 193s. N. M. KNIGHT 2,122,415 I ULP SCREENING incarna Filed Jan. 3, 1936 4 Sheets-Sheet 5 Figllf 56 25? A sa sa 23 f \\\x\\\ v'3070. 30

. Y v 23 v E i 66 v 65167 2s i E 566 E 3| 3S lnvenor.

M. Kn ig hT AJuly 5, 1938. l N. M.v KNIGHT 2,122,475

, PUL? SCREENING CHINE Filed Jan. 3, 1936 y 4 Sheets-Sheet 4 Fig@ I 4 lnvenTov 4 Nelson MKnghT 43 5 bymMkZ-MM Patented July 5, 193i' PATENT OFFICE PULP SGREENI'IG MACHINE Nelson M. Knight, Weymouth Heights, Mass. A Application January 3, 1936. Serial No.'57,378

17 Claims.

This invention relates to pulp screening machinesand particularly to machines of the type illustrated in my Patent No. 2,003,150, dated May 28, 1935.

The pulp screening machine shown in said patent comprises a casing having an inlet for unscreened pulp and an outlet for the screened pulp,a screen within the casing through which the pulp passes as it flows from the inlet to the outlet, said screen having a plurality of baille plates rigid therewith, and pulp-pulsating plates situated between the baille plates and movable toward and from the latter, the movement of the pulsating plates relative to the baille plates l serving to force the pulp back and forth through the screen as it flows from the inlet toward the outlet.

InA the device of said patent the pulp-pulsating plates are given their vibrating movement by an eccentric, as a result of which they have a simple harmonic movement, the movement of said pulsating plates relative to the baille plates being relatively slow'at the beginning and ending of each stroke and relatively rapid at the mid portion of the'stroke.

This uneven relative movement between the pulsating plates and the baille plates produces an uneven pulsation of the pulp through the screen, and as the pulsating plates are vibrated relatively rapidly, such uneven motion subjects both sets of plates to considerable strain.

-It is one of the objects of the present invention to provide a novel construction by which a more even relative movement Vwill be produced between the pulsating plates and the baille plates notwithstanding the fact that the pulsating plates have the simple harmonic motion resulting from being actuated by an eccentric or crank. This end is accomplished by providing screensupporting means which permits the screen to yield slightly in the direction of the movement of the pulsating plates so that as the speed of movement of the pulsating plates increases from the beginning of each stroke to the center thereof the pressure to which the baille plates are subjected will cause a yielding movement of the screen in the same direction as that of the pulsating plates, although of less extent, with the result that the relative movement between the two sets of plates will be a much more even and uniform movement than where the baille plates are xed or stationary as in the device illustrated in said patent.

In said patent the pulp screen is shown as a cylindrical screen and a plurality of screencleaning runners are provided on the inlet side of the screen which are given a rotative movement about the screen for the purpose of assisting in keeping the screen clean.

Another feature of my invention relates to an 5 improved construction of the screen-cleaning elevment.

Another feature of the invention relates to an improvement in the means for giving the simple harmonic movement to the pulsating plates by which the amplitude of vibrating movement of the plates may be readily changed from the exterlor of the machine. l

Other features of the invention relate to various improvements in pulp screening machines which will be more fully hereinafter set forth and will then be pointed out in the appended claims.

In the drawings:

Fig. 1 is a vertical sectional View through a pulp screening machine embodying my invention.

Fig. 2 is a section on the line 2-2, Fig. l.

Fig. 3 is a view showing one section or unit of the screen-cleaning element construction.

Fig. 4 is a View of the driving mechanism for the pulsating plates and the runners with parts brokenout to better show the construction.

Fig. 5 is a section on the line 5 5, Fig. 4.

Fig. 6 is a side view of the pulp screening ma. chine with one of the plates of the casing removed to give access to the screen-cleaning element.

Fig. 7 is an enlarged fragmentary sectional view showing the operation of the resilient support forthe screen. l

Figs. 8 and 9 are diagrammatic views illustrating the manner in which the eccentric for operating the pulp-pulsating plates can be adjusted to vary the amplitude of movement.

Fig. 10 is a fragmentary perspective view showing a detail of the sectional shaft 29. 40

Fig. 11 is a fragmentary view showing the two sections of the shaft 29 connected together.

In the drawings I indicates generally the casing of the machine which is shown as a vertical cylindrical casing having an upper head 45 2 provided with an inlet 3 for the unscreened` pulp and also provided with the lower head 4 having a discharge 5 for the screened pulp. This casing is supported on suitable legs or supports iand the upper head 2 has attached thereto a bearing member 1 having the inlet passage 8 through which the unscreened pulp is delivered to the inlet 3.

The casing I may be made in any appropriate way and as herein shown it comprises a plurality of curved plates 9 which are connected to vertically-extending post members I Il, there being four of these post members and consequently four plates 9. 'Ihe posts are shown as having a channel-iron shape and the plates 9 have ilanges II at their vertical edges which mate and are clamped to the flanges of the channeliron posts I by means of clamping bolts I2. With this construction the interior surface of the casing I is formed partly by the plates 9 and partly by the inner faces of the posts I8.

The screen which is situated Within the casing is indicated at I3 and it is shown as having a cylindrical screening wall which is connected at its upper end to an upper non-perforated screen head I4 and at its lower end to a lower screen head I5 that is provided with an outlet opening I6 registering with the discharge opening 5. the discharge opening I6 thus communicating with the interior of the cylindrical screen. The unscreened pulp thus flows into the casing and through the screen I3, thence through the outlet I6. The screen I3 has a plurality of baille plates I'I rigid therewith and preferably extending at right angles to the screen wall and situated between these baiile plates are pulp-pulsating plates I8 mounted for movement toward and from the baille plates. This relative movement of the pulsating plates I8 and baille plates causes the pulp to be pulsated or forced back and forththrough the screen as it flows frein the inlet to the outlet inthe manner described in my above-mentioned patent'. In the construction herein shown the baille plates II are annular plates situated on the inside or delivery side of the screening wall I3 and are rigidly connected at their periphery to said screening wall. These plates -are held spaced from each other by means of spacing elements I9 and the spacing elements are retained in position by means of tie rods 2U which extend through the spacing elements and tie the upper and lower heads I4 and I5 together. The spacing elements I9 extend through apertures 2l formed in the pulsating plates I8. The pulsating plates are rigidly secured to an axially-situated spindle 22 as in the above-mentioned patent. This spindle has two sets of radially-extending arms 23, each set of arms carrying one of the pulsating plates I8. The other pulsating plates are rigidly connected to these two pulsating plates by means of tie rods 24 which extend through all of the pulsating plates and which tie together the top and bottom plates, and spacing elements 25 through which the tie rods pass and which hold the pulsating plates properly spaced. These spacers 25 extend through openings formed in the baille plates I1 as described in the above-mentioned patent.

The lower end of the spindle 22 is mounted for axial reciprocation in a bearing 26 carried by the lower head I5, said bearing being supported in a hub s2 of a spider member integral with the head I5 and having radial arms 2'I, the space between the arms forming the outlet passage I6. This spindle 22 is connected at its upper end to an eccentric 28 on a drive shaft 29 that is mounted in suitable bearings carried by the bearing member 1. 'Ihe eccentric 28 has the usual eccentric strap 38 which is connected to the spindie 22 through the arms or links 3l.

The shaft 29 may be driven in any suitable way and as herein shown power for .driving the shaft is furnished from a suitable motor 32 carried on a bracket 33 secured to the bearing member 1. The motor shaft 34 has a belt pulley 35 thereon which is belted to a pulley 36 on the shaft 29 through the medium of a driving belt 31. The upper head I4 of the screen has a bearing 38 through which the spindle 22 extends. The spindle 22 is keyed to the bearing sleeve 26 through the medium of a key 94. The ends of the key are provided with fingers 93 which engage the bearing and thus retain the key in place. The key-94 permits vertical reciprocation of the spindle 22 but prevents rotative movement thereof.

As stated above the motion given to the pulsating plates I8 by the eccentric 28 is a simple harmonic motion in which the movement of the pulsating plates at the beginning and ending of each stroke is relatively slow while the eccentric is leaving or approaching the dead center and is relatively rapid while the eccentric is midway between the two dead centers. If the baffle plates Vare stationary this uneven movement of the pulsating plates causes an uneven pulsay tion of the pulp through the screen plate and furthermore subjects the baille plates to a considerable strain at the time that the pulsating plates have their highest speed of movement.

In order to produce a more even relative movement between the pulsating plates and the baille plates and thereby to relieve the plates from this undue strain and also to cause a more even pulsating movement of the pulp through the screen,/

Ition. One simple expedient is herein shown which is especially adapted for a screen pulp in which the screen has a vertical arrangement. Y

This means comprises yielding supports on which the screen rests and which are capable of yielding te' allow a slight downward movement ef the screen during the downward movement of the pulsating plates and which provide for a corresponding upward movement' of the screen during the upward movement oi the pulsating plates, the movement of the screen in each direction, however, being less than that of the pulsating plates so that the required relativev movement will be produced rbetween the pulsating plates and baille plates. In the construction herein shown the screen is supported on a plurality of spherical supporting elements 39 in the forniv of rubber balls which rest in seats 48 mounted onfthe lower casf ing head 4. The lower head I5of the screen is provided with seat members 4I having on their under faces spherical recesses to receive the balls 39. These seat members 4I are shown as retained in position by the tie rods 28, said tie rods being screw-threaded at their upper ends into the upper screen head I4 and extending through the lower screen head I5 and being screw-threaded into the seats 4I. The head I5 lis provided with a'tubular neck portion 42 which ts within an opening formed in the lower casing head 4, said neck being capable of axial movement through the opening. 43 indicates a bearing of Babbitt metal or other similar material to provide a tight slip joint and 44 indicates a ring of rubber or other yielding material which surrounds the neck 42 and is confined between the lower head 4 of the casing and a shoulder formed on the lower head I5 of the screen.

80 indicates a spring encircling the spindle 22 situated between the hub 82 of the spider 21 and the hub 8l of the lower set of arms 23. This spring will preferably be under some compression when the pulsating plates are at the highest point in their travel and during each downward movement of the spindle 22 said spring will be compressed somewhat.

'Ihe upper head I4 of the screen carries a cushion member 4G of rubber which is shown as faced with a metal plate 41, the latter having bearing against the hub portion' of a rotating runner-carrying member 48 by which lthe rotary runner above-referred to and presently to be described is supported.

With this construction assuming that the eccentric 29 is on its upper dead center then the\ runner plates and baffle plates will have the relative position shown in full lines in Fig. "I, the pulsating plates being relatively close to the baffle plates above themy and at a maximum distance from the baille plates below them. -As the pulsating plates are moved downward by the eccentric 28 the speed of downward movement increases progressively from zero at the starting point to a maximum speed at the mid-stroke and then decreases progressively from the mid-stroke to the lower end of the stroke. As the pulsating plates move downwardly the pulp between each pulsating plate and the baille plate below it is subjected to pressure tending to force the pulp outwardly through the screen and at the same time a suction will be produced between each pulsating plate and the baille plate above it tending to draw the pulp inwardly through the screen. As each pulsating plate moves upwardly the pulp be- Ltween it and the baffle plate immediately above will be subjected to pressure, tending to lforce the pulp outwardly through the screen while a suction will be produced beneath each pulsating plate tending to draw the pulp inwardly through the screen, this being the same operation as that described in my above-mentioned Patent No.

With the construction hereinillustrated during the downward movement of the pulsating plates the downward pressure produced on the baille plates through the medium of the pulp together with the pressure applied to the lower head I5 of the screen through the spring 88 will cause the yielding supports 39 to yield downwardly, thus permitting the downward movement of the screen as a unit, as shown in Fig. 7, wherein the full lines show the relative position of the pulsating plates and the baffle plates when the pulsating plates are at the upper end of their stroke, and the dotted line positions represent the position of the pulsating plates during their downward movement and the corresponding position which the screen and the baille plates have due to the downward pressure thereon and the fact that the screen is yieldingly supported.

As the pulp-pulsating plates I8 move downwardly from the full line position toward the dotted line position they subject the pulp between them and the baille plates below them to pressure which istransmitted to the baffle plates. This pressure not only causes the pulp to be forced outwardly through the screen but cooperates with the downward pressure against the screen through the spring 8D to cause the resilient or yielding balls 39 to yield downwardly, as shown in dotted lines, Fig. 7. Hence, during the downward movement of the pulp-pulsating plates the screen will have a slight downward movement and such downward movement ofthe screenwlll occur largely while the pulp-pulsating plates I8 are moving Amost rapidly at the middle portion of their stroke.

As the operating eccentric 28 passes its low center and thepulp-pulsating plates begin to move upwardly, the pressure of the spring 80 will gradually be relaxed and the resiliency of the rubber supports 39 will cause the screen and baille plates to move upwardly again during the upward movement of the pulp-pulsating plates. 'I'he spring 80, together with the cushion member 46, serves to cushion the upward movement of the screen.

With this construction, therefore, the screen itself has an up-and-down movement along with the up-and-down movement of the pulp-pulsating plates, although the amplitude of the movement of the screen and baille plates is less than that of the pulsating plates. This construction provides a relatively even relative movement between the pulp-pulsating plates and baille plates notwithstanding the simple harmonic movement of the pulp-pulsating plates.

The screen-cleaning element which rotates about the exterior of the screen for keeping the latter clean is indicated generally at 49, and as stated above it is carried by a rotating disk or support 48. This support 48 is secured to the lower end of a sleeve 50 which extends through and has bearing in the bearing member 1 and is provided at its upper end with a worm` gear 5I which meshes with and is driven by a worm 52 on a shaft 53 that is mounted in suitable bearings 54. This shaft 53 has a sprocket wheel 98 thereon which is connected by a sprocket chain 55 to a sprocket wheel 56 on the shaft 29, this construction being similar to that shown in my above-mentioned patent.

The screen-cleaning element 49 is formed with a plurality of spirally-arranged runners 51, and it is divided vertically at 9I into separate units, any one of which is of a size to be removed through the space provided when any one of the plates 9 is removed. Each section or unit of the screen-cleaning element is made up of a plurality of runner sections 51 having an inclined or spiral arrangement shown in Figs. 3 and 8, the runner sections of any unit being tied together by means of tie rods 58. Each runner sectionA is formed with two bosses 59 through which the tie rods 58 extend and these bosses 59 are of sufiicient length so that they hold the runners properly spaced from each other. The upper end of each tie rod 58 is screw-threaded into the lower end of a nut 60 and the lower end of each tie rod screws into another nut 6I. The nuts 60 at the upper end of the tie rods are detachably secured to the plate or disk 48 bymeans of clamping screws 82. 83 indicates a ringwhich is clamped to the under side of the lower nuts IiI by means of clamping screws 84.

The separate sections or units of the screencleaning element preferably have a circumferential dimension `slightly less than that of any plate 9, and as herein shown the screen-cleaning element is made up of live of such units.

If it is necessary or desirable to remove any unit of the screen-cleaning element this can be easily done by removing one of the plates 9 and then backing off the screws 62 and 64 for said unit until the screws are free from the nuts SII and 6I. When this has been done the unit can be removed as a single structure because the runner sections 5l remain clamped together by the tie rods 58 and the nuts 60, 6|. This construction facilitates the assernbly of the device as Well as any necessary repa1rs.

The machine herein shown also provides means by which the amplitude of vibrating movement of the pulsating plates I8 can be Varied, this being accomplished by varying the eccentricity of the operating eccentric 28. The eccentric 28 is a double eccentric having the two eccentric portions and two eccentric straps 30, as shown in Fig. 4, 4each eccentric strap being connected through a link 3| to the spindle 22. These eccentrics 28 are formed on a sleeve 65 which is mounted for rotation on an eccentric portion 66 of the shaft 29 and is adapted to be clamped to said shaft in different angular positions. The

shaft 29 is a divided shaft and comprises the sec` tion 29a to which the driving pulley 36 is secured and the section 29h to which the sprocket wheel 56 is secured, the division between the sections being wtihin the eccentric sleeve 65 so that the eccentric portion 66 of the shaft is formed partly on the section 29a and partly on the section 29h. Thetwo sections 29a, 29h are coupled together to rotate as a unit through the medium of a coupling member 6l which is received in slots 98 formed in the adjacent ends of the two shaft sections.

Means are provided which are accessible from the end of the shaft for clamping the eccentric sleeve 65 to the shaft or unclamplng said sleeve from the shaft whenever it is desirable to adjust it to change the amplitude of vibration of the pulsating plates. This eccentric sleeve 65 is confined between two flanges 68 formed on the two shaft sections 29a, 29h and the shaft section 29D has a clamping bolt 69 extending axially thereof which extends through the coupling member 61 and screws-into the end of the shaft section 29lb as 'shown at 10. The shaft sections are spaced slightly from each other at the adjacent ends and the coupling member 61 is of a size to permit a slight movement of the shaft sections toward each other. When the clamping bolt 69 is tightened the two shaft sections are drawn toward each other thereby clamping the eccentric sleeve 65 firmly between the flanges 68. W'hen the two eccentrics 28 and 66 are adjusted so that the eccentricity of each is on the same side of the axial line of the shaft, as shown in Figs. 5 and 8, then the amplitude of movement of the pulsating plates will be that given by` the two eccentrics combined. On the other hand, if the two eccentrics 28 and 66 are adjusted so that they oppose each other then the amplitude of movement of the pulsating plates will be that resulting from the difference between the throws of the two eccentrics, and if the two eccentrics have the same throw then by adjusting them so that they oppose each other the rotation of the shaft 29 will produce no vertical movement in the spindle 22. Whenever it is desired to make an adjustment in the amplitude of movement of the pulsating plates the clamping bolt 69 is lbacked off suiilciently to relieve the clamping pressure on the eccentric sleeve 65 and the operator then turns the shaft 29 through the medium of the wheel 16. The friction of the eccentric straps 30 on the eccentrics 28 will hold the latter from turning with tho shaft 29 after the eccentric sleeve 65 has been unclamped so that by turning the shaft 29 the two eccentrics can be adjusted into any desirable relative position to give the desired amplitude of movement of the pulsating plates. When the desired adjustment has been effected the clamping bolt 69- is tightened thereby clampingthe sleeve 65 to the shaft 29 in its adjusted position.. The fact that the clamping bolt 69 is accessible from the end of the shaft facilitates -greatly'the operation of making the desired adjustment in the eccentric. I claim. 1. A pulp screen comprising a casing having .an intake for unscreened pulp and an outlet for screened pulp, a vertical screen situated between -the inlet and outlet and through which the pulp flows, said screen having baille plates extending therefrom, pulp-pulsating plates situated between the baille plates, means to move the pulsating plates toward and from the baille plates, thereby causing the pulp to be forced back and forthv through the screen as it flows from the inlet to 'the outlet, and a support for the screen yieldable `in the direction of movement of the pulsating baille plates, means to move the pulsating plates' toward and from the baille plates, thereby causing the pulp to be forced back and forth through the screen as it flows from the inlet to the outlet, and resilient support for the screen yieldable in the direction of movement of the pulsating plates.

3. A pulp screen comprising a casing having an intake for unscreened pulp and a screened pulp outlet, a screen situated between the inlet and outlet, said screen having baille plates extending therefrom on the delivery side thereof, pulp-pulsating plates situated between the bafile plates, means to move the pulsating plates toward and from the baille plates, thereby causing `the pulp to be forced back and forth through the screen as it flows from the inlet to the outlet, said screen being movable in the direction of movement of the pulsating plates, and resilient means to resist such movement of the-screen.

4. A pulp screenv comprising a casing having a pulp inlet and a screened-pulp outlet, a screen situated between the inlet and outlet, baille plates rigid with the screen, pulp-pulsating plates situated between the baille plates,`means to move the pulsating plates toward and from the baille plates, thereby causing the pulp to be forced back and forth through the screen as it flows from the inlet to the outlet, and means for supporting the screen which permits it to have a limited movement in the direction ofmovement of the pulsating plates.

5. A pulp screen comprising a casing having a pulp inlet and a screened-pulp outlet, a screen situated between the inlet and outlet, baille plates rigid with the screen and extending therefrom, pulp-pulsating plates situated between the baille plates, means to move the pulp-pulsating plates toward and from the baille plates, thereby causingthe pulp to be forced back and forth through the screen as it ows from the inlet to the outlet, and a support for the screen yieldable in the direction ofthe movement of the pulsating plates.

6. A pulp screen comprising a casing having a pulp intake and a screened-pulp outlet a cylindrical screen within the casing, baille plates rigid with the screen and situated on the delivery side thereof, pulp-pulsating plates situated between the baille plates, means to vibrate the pulsating plates toward and from the baille plates, and yielding means supporting the screen and permitting limited movement thereof in the direction of vibration of thepulp-pulsating plates.

'7. A pulp screen comprising a.A casing having a pulp inlet and a screened-pulp outlet, a continuous-walled screen within the casing through which the pulp ows inwardly, baille plates rigidly secured to the screen on the inside thereof, pulp-pulsating plates between the baille plates, means to vibrate the pulp-pulsating plates toward and from the baille plates, and yielding screen-supporting means permitting yielding movement of the screen in the direction of movement of the pulp-pulsating plates.

8. A pulp screen comprising a casing having a pulp inlet and a screened-pulp outlet, a screen within the casinghaving a vertical screening wall, baffle plates rigidly secured to the screen on the delivery side thereof, pulp-pulsating plates situated between the baflle plates, means to vibrate the pulp-pulsating plates in a/vertlcal direction, and a vertically-yielding support for the screen.

9. A pulp screen comprising a casing having an intake for unscreened pulp and an outlet `for screened pulp, la screen situated between the inlet and outlet and through which the pulp flows, said screen having baille plates extending therefrom, pulp-pulsating plates situated between the baille plates, means to move the pulp-pulsating plates toward and from the baille plates, thereby causing the pulp to be forced back and forth through the screen as it flows from the inlet to the outlet, a yielding support for the screen and a spring interposed between said screen and the pulp-pulsating plates and resisting relative movement in one direction between said plates and screen.

10. A pulp screen comprising a casing having a pulp inlet and a screened-pulp outlet, a screen within the casing having a vertical screening wall, baille' plates rigidly secured to the screen on the delivery side thereof, pulp-pulsating plates situated between the baille plates, means to vibrate the pulp-pulsating plates in a vertical direction, a vertically-yielding support vfor the screen, and a spring interposed between the screen and the pulp-pulsating plates and resisting downward movement of said plates relative to the screen.

11. A pulp screen comprising a casing having an inlet and an outlet, a cylindrical screen through which the pulp flows inwardly, a rotary screen-cleaning element encircling the screen, said element comprising a plurality of runners spiralling about the screen, each runner having a plurality of spacing bosses which are in line with and engage corresponding bosses on the adjacent runners, tie rods extending through the alined bosses and clamping the runners together, a rotary supporting member coaxial with the screen at one end thereof, and means to secure said runner element to said supporting member.

12. A pulp screen comprising a casing having an inlet and an outlet, a cylindrical screen between the inlet and outlet and through which the pulp ows inwardly, a rotary screen-cleaning element encircling the screen, said element comprising a plurality of runners spiralling about the screen, tie 'rods extending parallel to the axis of the screen-cleaning element and rigidly connecting the runners together, said screencleaning velement being divided in a, plurality of places along lines substantially parallel to the tie rods of the cylindrical screen thereby to form separate screen sections, there being atleast one of said tie rods in each section, a rotary supporting member coaxial with the screen at one end thereof, means to rotate said member, and means for independently attaching each section of'the screen-cleaning element to said supporting member.

13. A pulp screen comprising a casing having an inlet and an outlet, a cylindrical screen through which the pulp flows inwardly, a rotary screen-cleaning element encircling the screen, said element comprising a plurality of runners spiralling about the screen, each runner having a plurality of apertured bosses, tie rods extending through said bosses and rigidly connecting the runners, nuts screw-threaded to the ends of -each tie rod and by which the runners are clamped together, a rotary supporting member coaxial with the screen, and bolts carried by said supporting member and screw-threaded into the nutsat one end of the screen-cleaning element thereby securing said element to said supporting member.

14. A pulp screen comprising a casing having an inlet and an outlet, a cylindrical screen through which the pulp flows inwardly, a rotary screen-cleaning element encircling the screen, said element comprising a plurality of runners spiralling about the screen, the runners having apertured bosses by which they are spaced from each runner, tie rods extending through said bosses, clamping nuts screw-threaded to the ends of the tie rods, said screen-cleaning element being divided longitudinally of the screen in a plurality of places, a rotary supporting member coaxial with the screen, and bolts carried by said member and having screw-threaded engagement with the clamping nuts at one end of the screencleaning element, whereby each section of the screen-cleaning element can be removed from the supporting element independently.

15. A pulp screen comprising acasing having an inlet and an outlet, a cylindrical screen through which the pulp'flows inwardly, a rotary screen-cleaning element encircling the screen, said element comprising a plurality of parallel runners spiralling about the screen, each runner being divided into a plurality of separate sections with the ends of the sections of any runner lined up with the ends of the correspondingsections of the other runners along lines extending substantially parallel to the axis of the screencleaning element, means for rigidly connecting together the corresponding runner sections of all runners, said connected corresponding runner sections forming separable sections of the screencleaning element, a rotary supporting member coaxial with the screen at one end thereof, and means for separately and detachably securing each section of the screen-cleaning element to Asaid rotary supporting member.

16. A pulp screen comprising a casing having a pulp intake and a screened-pulpoutlet, a cylindrical screen within the casing, baille plates side thereof, pulp-pulsating plates situated between the baille plates, means to vibrate the pulsating plates toward and from the baille plates, and yielding means supporting the screen and permitting limited movement thereof in the. direction of vibration of the pulp-pulsating plates but of less amplitude than that of said plates.

` rigid with the screen and situated on the delivery together the corresponding runner sections of all the runners, each set of connected-together runner sectidns forming a separable section of the screen-cleaning element, a rotary supporting member coaxial with the screen atrone endfthereof, an annular member at the other end of the screen, and means for separately and detachably securing each separable section of the screencleaning elementi to both the rotary supporting member and saldgannularfmembera NELSON M. KNIGHT. 

